1. Field of the Invention
The invention relates to an electrodynamic loudspeaker, especially a tweeter or mid-range loudspeaker, having omnidirectional emission of sound, said loudspeaker being made of two identical individual loudspeakers arranged on both sides of a plane of symmetry and having coaxial, oppositely directed drive units incorporating in each case
a permanent magnet fixed at a common carrier part, and PA1 a moving coil means (sometimes referred to as a voice coil wound on a bobbin) resiliently and yieldably held by a spider at said carrier part and rigidly fixed to a dome-like membrane in each case.
2. Prior Art
In the electrodynamic loudspeaker known from the French patent No. 1 146 757 a drive unit of each individual loudspeaker is arranged within hemispherical membranes, the moving coil means having one fifth of the diameter of the outer rim of the membranes. They are thus fixed only in their summit region at the respective membrane. This gives rise to irregular conditions of oscillation, the membranes deform themselves and at all events do not move as a rigid entity as intended. The influence of an additional spider has to be taken into account, too, as this spider connects the membrane along a circle of approximately half the diameter of the outer rim to the permanent magnet of the drive unit. To summarize, during movement of the membrane by the attached moving coil, the outer rim sections of the membrane are left behind and partial vibrations are formed across the membrane. They are the origin of secondary emissions of sound, which do not coincide with the original sound to be reproduced.
In addition, the known electrodynamic loudspeaker does not allow for an optimal omnidirectional emission of sound, because its carrier part is continued outwards in the form of a ring. The drive units are connected to each other in such a way, that the two membranes always perform movements in the same direction. The individual loudspeakers cannot reproduce different sound signals.
U.S. Pat. No. 3,456,755 shows an hydraulic loudspeaker which is also assembled from two semispherical individual loudspeakers having electrodynamic drive units. In this device, the moving coil means is not rigidly connected to the membrane. Further, the diameter of the moving coil means amounts to only one eighth of the diameter of the outer rim of the membrane.
U.S. Pat. No. 3,393,767 shows a loudspeaker of spherical shape as seen from the exterior. Two loudspeakers having cone shaped membranes are mirror-symmetrically arranged. An omnidirectional emission of sound cannot be obtained, as the sound emission of each individual loudspeaker, having a cone shaped membrane, is effected in a preferred direction.
Finally U.S. Pat. No. 4,472,605 shows an electrodynamic loudspeaker constructed in a similar way as the loudspeaker mentioned above. This device is exclusively intended for low sound frequencies. In this loudspeaker the relation of the diameter of the moving coil means and the diameter of the outer rim of the semispherical membrane is one and nine. In order to avoid that the proportion of the membrane is too-locally confined, semispherical transmission parts are arranged between the moving coil and the membrane, so that the membrane indeed is rigidly connected to the moving coil means, but this connection is not achieved directly but by means of a transmission part arranged inbetween.
These known spherical loudspeakers do not give satisfactory results in their emission of sound. Secondary vibrations of the dome-shaped membranes exist and are not sufficiently suppressed, and the propulsion is too weak compared to the surface of the membrane. To sum up the results obtained in sound emission are unsatisfactory.
In the tweeter and mid-range loudspeakers of the electrodynamic type predominantly used at present the diameter of the moving coil means generally equals the diameter of the outer rim of the membrane. This provides for an efficient propulsion, secondary resonances of the membrane are extensively reduced, and the membrane oscillates even at high sound frequencies mainly as a rigid body. These loudspeakers having dome-shaped membranes on the other hand do not provide for an omnidirectional emission of sound.
It is here that the invention provides a remedy. It is the object of the invention to avoid the draw-backs of the known electrodynamic loudspeakers having omnidirectional emission of sound and to provide, on the basis of the construction principles of the known dome loudspeakers, for an efficient precisely reproducing electrodynamic loudspeaker of the kind indicated above having an omnidirectional emission of sound, wherein said loudspeaker is of a simple construction and may be easily fixed to a supporting part.